Dust Emission from Protostars: the Disk and Envelope of HH 24 MMS

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Abstract
High-resolution imaging of the protostar HH 24 MMS at wavelengths of 7 mm and 3.4 mm shows the dust emission to originate from two components: an unresolved disk and an extended envelope. The envelope is an order of magnitude more massive than the disk, suggesting that HH 24 MMS is very young, since the fraction of circumstellar material in an extended component probably decreases with the age of the forming star. For the disk, the frequency dependence of the dust mass opacity coefficient, β, is 0.68 ± 0.12, significantly lower than the interstellar medium value of 2. In the envelope β is less well constrained but must lie in the range 0 to 1.9. Emission from the disk dominates at wavelengths longer than 3 mm, but the far-infrared emission is relatively weak. This suggests that the envelope is optically thick at wavelengths as short as 60 μm and obscures the disk.